Shell Search and Replace variable in configuration file using sed

[fumanchu]

Hello,

I have tried and tried messing around with sed and regular-expressions but I just cannot find a solution. So I thought I would post this to the forum for some help...

I am in need of searching for and replacing, name/value pairs in a configuration file. An example would look something like this...

variable = value # Comment.

Nothing too complex... However, the issue is that the file can be hand edited, so spacing at the beginning and in between each piece can be variable...

Any idea on the sed syntax needed to search for a variable and replace its value?

Many thanks,

 

[yuripv79]

What do you have already that does not work?

 

[Charlie_]

I don't know much about sed, but I tried it.
sed -E 's/((^|[[:space:]]+)variable[[:space:]]*=[[:space:]]*)[^[:space:]]+/\1value/' filename
Does it work?

 

[fumanchu]

I don't know much about sed, but I tried it.
sed -E 's/((^|[[:space:]]+)variable[[:space:]]*=[[:space:]]*)[^[:space:]]+/\1value/' filename
Does it work?

Unfortunately, that does not seem to work... Here is my script so far.

#!/bin/sh
total_memory=$( sysctl -n hw.physmem | awk '{ byte =$1 /1024/1024/1024; print byte }' )
echo $total_memory
quarter_memory=$(printf "%.0fGB" $(echo $total_memory*.25 | bc))
echo $quarter_memory
#sed -i '' -E "s/\s\(shared_buffers\s=.*$/shared_buffers = $quarter_memory/g" ./postgresql.conf
sed -i '' 's/((^|[[:space:]]+)shared_buffers[[:space:]]*=[[:space:]]*)[^[:space:]]+/\1$quarter_memory/' ./postgresql.conf

I end up getting the following error:

sed: 1: "s/((^|[[:space:]]+)shar ...": \1 not defined in the RE

 

[Charlie_]

sed -E -e "s/((^|[[:space:]]+)shared_buffers[[:space:]]*=[[:space:]]*)[^[:space:]]+/\1\\$quarter_memory/" -i '' ./postgresql.conf
Use -E option.

Edit: -e added.

 

[astyle]

I usually practice a sed command on something where it's easy to see the result - and doesn't mess up the config file. Helped me a LOT.

 

[fumanchu]

I usually practice a sed command on something where it's easy to see the result - and doesn't mess up the config file. Helped me a LOT.

I am trying this out on a copy of the configuration file :

 

[fumanchu]

sed -E "s/((^|[[:space:]]+)shared_buffers[[:space:]]*=[[:space:]]*)[^[:space:]]+/\1\\$quarter_memory/" -i '' ./postgresql.conf
Use -E option.

Using the -E option does work and the variable is replaced; however, the replacement is only shown on the screen. The file is not actually modified...

 

[Charlie_]

The -e option was missing.

 

[fumanchu]

The -e option was missing.

Wow... how could I have missed that... but I did. Many thanks, your solution worked!

 

[balanga]

Just as an aside, you might want to go to Edit thread (on the right of your first post next to Watch) and mark it as Solved

 

[zirias@]

Probably a bit shorter and easier to read selecting the line by the name, something like
sed -i '' -e '/^variable/s/=[^#]*/= $value /'